Micro-lysimeters containing undisturbed soil samples placed
between plant rows (Daamen et al., 1993) were used to determine
soil evaporation. The micro-lysimeter casing and the pipe lining
the holes, in which the micro-lysimeter was mounted, were both
constructed from un-plasticised PVC pipes. These micro-lysimeter
were 11 cm in internal diameter and 15 cm in length. The liner tube
was 12 cm in internal diameter and the same length. Care was taken
to minimize the gap between the microlysimeter and the liner. The
weight loss was recorded by an electric scale (sensitivity, 0.01 g)
put into the liner tube. Both tubes were put into the pit where
undisturbed soil had been taken. Soil cores were taken manually
by inserting the micro-lysimeter casing in the soil and then excavating
a slightly oversized core of soil to a depth 2–3 cm below the
base of the core. When the required depth was reached the cores
were trimmed flush at the base and were placed on a sheet-metal
base plate and sealed with waterproof tape. The micro-lysimeter
was then mounted in a liner tube, with its surface slightly above the
soil surface. The micro-lysimeters in mulched plots were covered
with similar sand and gravel mulch or/and plastic film. Nylon gauze
was placed between the gravel and the soil to prevent them from
mixing. The prevention of evaporation by the nylon gauze was far
less than from gravel. Therefore, the effect of the nylon gauze on
evaporation was negligible. Two micro-lysimeters were installed
in every treatment to measure evaporation. Micro-lysimeters with
undisturbed soil were weighed at 08:00 every morning. Soil core
was renewed after 4 days for sand and gravel or plastic mulch treatments,
and after 2 days for unmulched treatments. However, the
core was immediately renewed after rainfall events.